1. Field of the Technology
The present disclosure is directed to the fields of dual hardness steels and methods of making dual hardness steels.
2. Description of the Background of the Technology
Roll-bonded dual hardness steel armor is a highly effective armor material. One example of this type of steel armor is ATI K12®-MIL Dual Hard armor plate, which is available from ATI Defense, Washington, Pa. USA. ATI K12®-MIL Dual Hard armor is disclosed as one embodiment in U.S. Pat. No. 5,749,140, which is incorporated by reference herein in its entirety. ATI K12®-MIL Dual Hard armor plate is a roll-bonded material having a high hardness front side and a softer back side. In use, the armor's hard front side breaks up and flattens an incoming projectile, and the softer back side captures and further absorbs the energy of the deformed projectile.
Although conventional roll-bonded dual hardness steel armor has substantial ballistic penetration resistance, it is difficult and expensive to produce the material. Complex post roll-bonding heat treatments and other processing are required to achieve desired mechanical and ballistic properties in conventional roll-bonded dual hardness steel armor. In particular, it is necessary to austenitize, oil quench, and temper the material subsequent to roll-bonding. In addition, these process steps can only be conducted on one small section of a roll-bonded plate at a time because excessive warping of the plate otherwise can occur due to differences in thermal expansion coefficients and transformation temperatures of the two roll-bonded alloys.
In addition, after heat treatment, conventional dual-hardness steel armor plates must undergo a complex flattening treatment. Only a limited number of manufacturing locations are properly equipped to carry out the flattening treatment. Also, the need to carry out the flattening treatment on plates effectively limits the size of conventional roll-bonded dual hardness steel armor plates to sizes no greater than about 20×20 inches (50.8×50.8 cm). Larger plates must be fabricated by joining together multiple smaller plates, substantially increasing part cost and fabrication time, as well as potentially negatively affecting the integrity of the part.
Accordingly, a need exists for a method of making roll-bonded dual hardness steel armor that does not require conventional post roll-bonding steps, such as austenitizing and oil quenching, and/or that reduces the need for tempering and complex flattening procedures for many applications. More generally, a need exists for an improved method of making dual hardness steel armor.